Electrolytic process for forming cadmium electrodes

ABSTRACT

The invention relates to a process for the preparation of sponge cadmium electrode material which comprises the steps of compressing the mixture of cadmium oxide and a finely divided inert electronic conductor at a pressure between about 1 psi and 100 psi, and subsequently electrolytically reducing the cadmium oxide to metallic cadmium in an alkaline electrolyte. Preferably the cadmium oxide is used in the form of a powder having a particle size between about 50 microns and 150 microns while the electrolytic conductor is preferably finely divided nickel powder or a metal in filamentary form such as steel wool, nickel wool, or electrolytic copper wool and is furthermore preferably used in a proportion amounting to between 5 and 45 percent by weight of the total mixture. Particularly good results are obtained when the compressing pressure is between about 1 and 4 psi.

United States Patent [191 Haines et al.

[451 Nov. 27, 1973 41 CADMIUM ELECTRODES [75] Inventors: Ronald L.Haines; Ian 11. S. Henderson, both of Ottawa, Ontario, Canada; FranklinSievenpiper, Brandon, Fla.

[73] Assignee: Her Majesty the Queen in right of Canada as representedby the Minister of National Defence [22] Filed: June 26, 1972 [21] Appl.No.: 266,240

Related US. Application Data [63] Continuation-impart of Ser. No 1,335,Jan. 8, 1970,

abandoned.

[52] US. Cl 204/115, 136/24, 204/292 [51] Int. Cl. C22d l/22, l-lOlm43/04 [58] Field of Search 204/292-293, 204/115, 35; 136/24, 2829, 67

[56] References Cited UNITED STATES PATENTS 2,830,108 4/1958 Peters136/24 3,062,908 11/1962 Salkind 136/24 3,048,644 8/1962 Euler 136/24Peters 136/24 Salauze 136/24 [5 7] ABSTRACT The invention relates to aprocess for the preparation of sponge cadmium electrode material whichcomprises the steps of compressing the mixture of cadmium oxide and afinely divided inert electronic conductor at a pressure between about 1psi and 100 psi, and subsequently electrolytically reducing the cadmiumoxide to metallic cadmium in an alkaline electrolyte. Preferably thecadmium oxide is used in the form of a powder having a particle sizebetween about 50 microns and 150 microns while the electrolyticconductor is preferably finely divided nickel powder or a metal infilamentary form such as steel wool, nickel wool, or electrolytic copperwool and is furthermore preferably used in a proportion amounting to between 5 and 45 percent by weight of the total mixture. Particularly goodresults are obtained when the compressing pressure is between about 1and 4 psi.

13 Claims, 7 Drawing Figures PAIENIEDnuvm ms 3; 775,213

SHEET 1 BF 4 I2 PRESSURE APPLIED TO TEST ELECTRODE SAMPLE PRIOR TOREDUCTION F I G. I

N LO BAHHO HSHVHDSIG .40 33m 01 NM PATENTEDNU'IPY I975 MINUTES TI I IEE"OF DISCHARGE CURVE CHARGE CURVE MINUTES TO "K EE" OF oIs 3775.273 SHEET2 BF 4 XI [NCO TYPE 255 CARBONYL NICKEL o2- INCO TYPE IOO CARBONYLNICKEL Ai- SHERRIT-GORDON TYPE 60-9 NICKEL I -STEEL WOOL FIBRE, 2/0GRADE L l I l l 1 l O 5 IO I5 3O PERCENT ADDED CONDUCTOR F I G. 2

Ioo-

5 o l l l l o 50 I00 i5O 20o PARTICLE SIZE DISTRIBUTION, MICRONS PMENYEUMN 2 71975 SHEET 3 OF 4 FIG.4

0 mo 7 5 m, O I O O O O O O O O A9503 mEm 3mm CADMIUM ELECTRODES Thisapplication is a continuation-in-part of our copending application Ser.No. 1,335, filed Jan. 8, 1970, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to sponge cadmiumelectrode materials for cells such as mercuric oxide-cadmium;

'mium hydroxide, and the electrolytic conductivity must be maintained bythe provision of adequate porosity in order to permit free access by thepotassium hydroxide electrolyte solution.

Sponge cadmium can be produced by electrolytic reduction inalkaline-solution of pressed pellets of cadmium oxide. The resultantmetallic cadmium cannot however be easily reoxidized electrolyticallybecause the oxidation product (cadmium hydroxide) is more voluminousthan the original cadmium oxide and is also a poor ionic and electronicconductor. Thus sponge cadmium, to be suitable as a battery electrode,must have adequate porosity to permit free access by the alkalineelectrolyte and to permit the formation of cadmium hydroxide withoutappreciable net volume change of the electrode. Further, it must possessa sufficiently high electronic conductivity to permit the oxidation of alarge fraction of the metal during battery discharge.

Conventional methods of fabrication of sponge cadmium are either costlyin that they involve a large number of steps and the use of relativelyexpensive materials such as mercury or copper, orthey lead necessarilyto a voluminous product because of the addition of cellulosic or othermaterials in an effort to maintain adequate porosity. In U.S. Pat. No.2,697,737, issued Dec. 21, 1954, Goldberg and Reid described arechargeable mercuric oxide-cadmium dry cell in which the anode was madeby compressing cadmium powder. The powder used was fairly coarse andmercury in quantities up to 20 percent by weight was added to the anodemass to form an amalgam therewith in order to yield a firmer pellet, andalso to make the cadmium more electrochemically available. In order toincrease porosity and maintain the required state of subdivision duringcharge-discharge cycling, Roberts, in U.S. Pat. No. 2,448,052, issuedAug. 31, 1948, described the use of expanders of cellulose, diatamaceousearth, kaolin or powdered porcelain in admixture with cadmium oxide.Such expanders give rise to a relatively voluminous product. Accordingto a more recent process described by Matsuno and Iwazaki in JapanesePat. No. 4020 issued May 26, 1959, porous cadmium electrodes areprepared from a mixture of 75% cadmium chloride and 25 percent zincchloride fused onto a sinter d pp substrate. The zinc chloride issubsequently leached out by sodium hydroxide solution and the porouscadmium chloride reduced to sponge metal. Although adequate porosity canbe obtained by this method, the expause and the number of steps involvedconstitute a considerable disadvantage coupled with the fact that theoperating conditions of the method are relatively difficult to control.In U.S. Pat. No. 2,830,108, issued Apr. 8, 1958, Peters describes thepreparation of sponge cadmium anodes from mixtures of cadmium, cadmiumoxide, and an inert metal (cg. nickel) powder compressed to 700 to 1,400kgs. per square centimeter, either in the presence or the absence of asupporting nickel screen or mesh. It has been found, however, that theresultant porosity of the electrodes made by this method is rather low.

lathe preparation of sponge cadmium electrodes, it has been found thatpressed pellets of cadmium oxide can be quantitatively reducedelectrochemically in 30% potassium hydroxide to sponge cadmium, but thatfollowing reduction quantitative electro-chemical oxidation does notappear to be possible, the maximum conversion efficiency correspondingto about l0% at the 20 hour rate. In order to improve the electronicconductivity of the active mass, carbonyl nickel powder (INCO type 255)in an amount of 10% by weight was mixed with cadmium oxide prior topelleting at pressures of 2,000, 3,000 and 4,000 psi. Similar pelletswere pressed without added nickel. The pellets, after pressing wereapproximately 10 millimeters in diameter and 5 millimeters in length.Qualitatively, the lower the pelleting pressure, the greater was theelectro-chemical reversibility found to be. The presence of nickelresulted in a further improvement so that a pellet with e.g. 10% nickelprepared at 2,000 psi delivered approximately 25% of its coulombiccapacity on discharge at the 20 hour rate.

SUMMARY OF THE INVENTION It has now been discovered that a verysatisfactory sponge cadmium electrode material can be prepared by theelectrolytic reduction of mixtures of cadmium oxide with a finelydivided inert electronic conductor, providing the mixtures are notcompressed too strongly prior to reduction. Electrodes prepared fromcadmium oxide, compressed at less than 100 psi., and particularly atfrom 1 to 4,psi., and electrolytically reduced in 30% potassiumhydroxide, showed much higher coulombic efficiencies (up to or more)than electrodes pressed at e.g. 2,000 psi. and the inclusion of means toimprove the electronic conductivity of the active mass by the use ofnickel powder, expanded nickel mesh, or commercial 2/0 grade steel wool,produced electrodes of considerable practical usefulness. Further, thismaterial can be produced either directly. as single cell electrodes orin the form of larger blocks, which may subsequently be cut into smallersegments as electrodes for incorporation into cells.

Thus, according to the present invention, there is provided a processfor the preparation of sponge cadmium electrodes which comprises thesteps of compressing a mixture of cadmium oxide and finely divided inertelectronic conductor, present in an amount of 5 to 25 percent by weightof the total mixture, at a pressure of at least 1 psi. but not exceedingpsi. and subsequently electrolytically reducing said cadmium oxide in analkaline electrolyte. In a preferred feature of the invention a cadmiumoxide/nickel mixture is employed. A preferred pressure range is from 1to 30psi while a still more preferred range is from 1 to 10 psi andparticularly from 1 to 4 psi. The cadmium oxide is preferably of lessthan microns in particle size, and

particularly from 50 microns or somewhat less up to 150 microns.

Although nickel powder having a density of less than 2 gm/cm,particularly less than I gm/cm is a preferred electronic conductor,other powders and finely divided forms of material such as iron powders,steel wool, nickel wool, copper wool, copper powder, graphite, carbonblack and the like may be used, provided that the material is inert atthe anode of a cadmium alkaline cell.

The cadmium oxide finely divided electronic conductor mixture inpractice has to be contained in a suitable mold or other container priorto the compressing step. Preferably this container is formed of an inertconductive material, particularly nickel, although it is prefectlypossible to use an insulating material if an electrical connection tothe compressed mixture is provided e.g. by inserting a wire, foil ormesh, preferably of nickel, into the container along with the powder tobe compressed or pressing same into the mixture after compression.

The mixture, after compression at the low pressure utilized inaccordance with the invention, particularly if only 1 to 4 p.s.i.g. isemployed can only be handled in its container until after electrolyticreduction. However, this presents no problem since the containercarrying the compressed mixture and provided with a suitable electricalconnection may be readily immersed in alkaline electrolyte such as a 30%aqueous potassium hydroxide solution and electrolytically reducedemploying for example a nickel foil anode.

The sponge cadmium produced in accordance with the invention is a softcoherent spongy mass which is quite readily handled withoutdisintegration and is easily cut and shaped, for example with a knife.When permitted to dry out, the reduced material becomes pyrophoric, andhence is normally handled whilst still saturated with potassiumhydroxide solution from the reduction step. Electrolytic connection, ifnot already present, is easily made to the sponge cadmium, e.g. byinsertion of a strip of nickel foil or wire when test electrodes havebeen cut from the reduced material. Cells constructed with spongecadmium electrodes produced in accordance with this invention aregenerally intended as primary cells and have a very satisfactory shelflife.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be describedfurther by way of example only and with reference to the accompanyingdrawings in which:

FIGS. 1 to 3 are graphs depicting compressing pressure vs. dischargetime; percentage added conductor vs. discharge time; and cadmium oxideparticle size distribution vs. discharge time respectively,demonstrating the coulombic efficiencies of various samples of spongecadmium electrodes prepared in accordance with the invention;

FIGS. 4 to 6 are graphs depicting discharge curves relating to the cellsreferred to below as Nos. 1 to 3 respectively;

FIG. 7 is a graph depicting discharge curves relating to cell Nos. 4 and5.

Experiments were carried out in order to assess the coulombic efficiencyof sponge cadmium electrodes prepared from cadmium oxide as a functionof (a) prereduction pelleting pressure; (b) type and percentage of addedelectronic conductor and (c) cadmium oxide particle size distribution,the results being shown as FIGS. 1 to 3.

All test specimens contained 3.2 gms of chemically pure cadmium oxidepowder 1,500 ma hrs) compressed to a pellet 18 mm diameter by 5 mmlength. The cells in which the pellets were prepared, reduced anddischarged consisted of 25 mm lengths of 18 mm internal diameter acrylictubing cemented to acrylic base plates. The weighed samples of testmaterial were compressed in the cell by means of a loosely fittingpiston which was loaded with weights to yield the desired pressure. Theloaded piston was left in place for a standard time (5 minutes) prior toits replacement by a nickel foil counter electrode and the addition of30% potassium hydroxide electrolyte. The pellet was reduced at 300 mafor 4 hours. This duration of current flow did not correspond tocomplete reduction of the cadmium oxide present, but represented theonset of vigorous hydrogen evolution for most samples at the relativelyhigh formation rate selected for electrodes of this thickness. Theresultant sponge cadmium was discharged at 300 ma to the knee of thedischarge curve, the e.m.f. with reference to a mercury-mercuric oxideelectrode, being recorded as a function of time.

The pelleting pressure was varied from zero to approximately 60 psi, andelectronic conductor content from zero to 45 weight percent. The typesof electronic conductor added were as follows: carbonyl nickel powder,INCO types 255 (apparent density 0.6 gm/cm) and (apparent density 1.5gm/cm hydrometallurgical nickel powder Sherritt Gordon type GO9(apparent density 2 gm/cm); steel wool (2/ 10 grade cut to give anaverage fibre length of 3 mm); carbon black; and graphite.

The first experiments were carried out on a mixture of cadmium oxide 25%INCO type 255 nickel powder. FIG. 1 shows a curve of the pelletingpressure prior to reduction versus minute of discharge to the knee ofthe discharge curve with vertical lines indicating the extent ofreproducibility of the capacity measurements. The delivered capacitydecreased somewhat below approximately 1 psi and above 4 psi. Thedecrease at the lower pressure is thought to be due to a lack ofelectronic contact, whereas at the higher pressures may be associatedwith a decrease in the electrolyte-retaining volume, making completedischarge dependent upon transport of potassium hydroxide into theactive mass and hence upon the ionic conductivity of the cadmiumhydroxide. Subsequent experiments were all carried out using apellet-forming pressure of 2 psi.

FIG. 2 illustrates the results obtained as a function of type and amountof electronic conductor added to the cadmium oxide. It is seen that onthe basis of weight percent of added electronic conductor, the pelletscontaining the very low density powder (INCO type 255) had run-out timesconsistently longer than with other additives, although these wereclosely approached by steel fibre additions for lower percentages ofadded electronic conductor. Other advantages of this nickel powder arethat it is relatively inexpensive and is readily mixed with cadmiumoxide to result in an exceptionally high electrode capacity per unitvolume. Steel fibre was found to be difiicult to handle in that prior tomixing, it had to be cut into very short lengths to prevent balling"during mixing. Furthermore sponge cadmium blocks containing steel fibrewere not as easily sliced as the nickel-containing material. However, ashereinafter described, when individual electrodes were made and thecadmium oxide was well distributed throughout a fibrous steel wool mass,very acceptable electrodes were obtained. The disadvantages of the moredense nickel powders are their costs in terms of effective concentrations and their lower electrode capacity per unit weight andvolume. Carbon additions to the cadmium oxide (not shown in FIG. 2)resulted in a substantially more voluminous electrode under theconditions of the present experiments, and were generally more difficultto handle. These observations suggested that the use of thehigherpelleting pressures required to make coherent samples of sponge Icadmium containing carbon, might result in pellets of rather lowporosity.

In order to investigate the effect upon capacity of the cadmium oxideparticle size distribution, a sample cadmium oxide powder was separatedinto fractions having the following particle sizes: (i) less than 45microns; (ii) 45 62 microns; (iii) 62-75 microns; (iv) 75-105 microns;(v) l05l50 microns; (vi) 150-l75 microns; and (vii) above 175 microns.

Testfelectrodes were prepared from, each fraction, using mixtures of 3.2grams cadmium oxide and 0.8 grams INCO type 255 carbonyl nickel powdercompressed into pellets at 2.0 psi prior to reduction. FIG. 3 showsdischarge time at 300 ma to the knee of the discharge curve (with thevertical height of the boxes indicating extent of reproducibility as inFIG. 11) as a function of particle size. These observations suggest anoptimum distribution in the range of 50 to 150 microns. The decrease indelivered capacity for particles less than 50 microns may beattributable to a decrease in the net electronic conductivity of theactive mass, and therefore could probably be improved by increasing thepelleting pressure e.g. up to 4 psi or even more, or the proportion ofnickel powder. The capacity decrease observed for larger particles wasanticipated, because the lack of porosity of cadmium produced byreduction of the large particles would be comparable with that ofpellets formed at higher pressure (see FIG. 11). It is believed that, inproduction, sieving to remove only the larger particles, namely over 150microns, is all that would be required. v

The fraction of cadmium utilized during discharge was found to bedependent to some extent upon the prepared from the 105 to 150 micronsfraction using 2.14 grams of cadmium oxide and 0.5 grams nickel powder,and otherwise treated as in the samples hereinbefore described. Whendischarged at 300 ma (3.3 hr. rate) the cadmium utilization to thedischarge curve knee was 65 percent of the theoretical value, whereasthe corresponding 3.2 gram sample, discharged at 300 ma (5 hr. rate),yielded less than 60 percent of the theoretical value.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A number of electrodes werefabricated and incorporated into test cells. The electrodeconfigurations selected for study were those compatible with (a) the Csize manganese dioxide alkaline cell (15 AH), (b) the 1,450 size (4.5All-I) mercuric oxide-zinc cell, and cells having electrodes 25 mm.square by approximately 6 mm. The cylindrical negative electrode sizescorresponding to (a) and (b) were: (a) 12 mm outside diameter, 30 mmlength; and (b) 28 mm outsidediameter, mm length.

Cell No. 1

The cadmium electrode used in this cell was made as follows:

Reagent grade cadmium oxide mixed with 25% by weight INCO type 255carbonyl nickel powder was packed dry into a X 50 mm Soxhlet extractorthimble loosely filled with 2/0 steel wool, and subjected to lowpressure (less than 10 psi). Thimble and contents were then transferredto potassium hydroxide solution for electrolytic reduction. Thecathodewas manganese dioxide. During the first cycle, this cell wasdischarged through a 10 ohm resistance hour rate), the discharge curvebeing shown in FIG. 4. This represents more than 75% of the cadmiumelectrode capacity. The cell was then recharged for 17 hours at 100 ma.During recharge, the negative electrode was reduced to cadmium with theevolution of hydrogen during overcharge, whereas the positive electrodewas oxidized from a lower valence state of Mn to MnO The cell wasshunted with diodes to limit the charging voltage to 1.4

' 1.5 volts to preclude the possibility of producing manganate. Eventhough the cell top was but crudely closed, there was no evidence ofelectrolyte having been forced from the cell by gas evolution. Whenrecharging on a number of subsequent cycles without diodevoltage-limiting, the capacity fell off suggesting that manganatemigration to the negative electrode had occurred.

- Cell No. 2

thickness of the pellet. For example, one electrode was The positive(manganese dioxide) electrode from a C cell was pulverized, moistenedand pressed in a mould at 15,000 psi to give a square electrode ofdimensions 25 X 25 X 6 mm, having a capacity of approximately 750 mahour. A piece of sponge cadmium of similar size was cut from stockelectrode fabricated as indicated for the electrode of Cell No. 1, butcut from a larger piece of material. This was assembled into a cell withthe manganese dioxide electrode using a Visking separator and an outersheath of polyethylene .film and masking tape. The 20 hours ratedischarge at room temperature is depicted in FIG. 5.

Cell No. 3

This cell used a Mallory 1450R mercuric oxide cathode and cell case andthe anode was prepared as for Cell No. l to give a sponge cadmiumelectrode of 25 mm diameter and 6 mm in length, with atheoreticalcapacity of approximately 3 amp hours. The electrolyte waslow carbonate 30% potassium hydroxide solution. The discharge curve ofthe cell at 40 is shown in FIG. 6.

Cell No. 4

This cell used the same electrolyte, cathode and case as cell No. 3 andthe anode used was prepared as follows: Reagent grade cadmium oxide wasmade up to a thin paste with water and caked on a piece of filter paperin a 30 mm diameter polypropylene suction filter having a loosely-packedlayer of 2/0 grade steel wool. The filter was transferred to potassiumhydroxide solution, and the cadmium oxide reduced electrolytically insitu. 2/0 steel wool was used to promote electronic conductivity. Thetheoretical capacity was approximately 3 amp hours. The discharge curvefor discharge at ma shown in FIG. 7 (Curve I) indicates a substantialand increasing polarization with time, but with 65% utilization of thecadmium.

Cell No.

A portion of the mercuric oxide cathode from a fresh Mallory 1450R cellwas crushed and then compressed at 15,000 psi to form an electrode ofdimensions 25 X 25 X 5 mm. This electrode was used in a cell with twosimilarly shaped pieces of sponge cadmium cut from a larger piece ofmaterial as indicated for the electrode of Cell No. 2 using a Viskingseparator and 30% potassium hydroxide electrolyte. The outer containerwas formed from a layer of polyethylene film held in place by rubberbands. The 40C discharge curve at 30 ma is shown in FIG. 7 (Curve ll).Following this, the discharge of the cell was continued at roomtemperature at 40 ma. The voltage was very constant at 0.86 v for atleast 12 hours. Following this discharge, the cell was recharged for 4hours at 300 ma and discharged again at room temperature at 43 ma. Aflat discharge was obtained for 43 hours, after which time the voltagedropped rapidly.

EXAMPLE 1 When the cadmium oxide-nickel mixture referred to in thedescription of cell No. l was packed as described into an expandednickel mesh basket, the discharge capacity increased to about 80% at thehour rate.

EXAMPLE 2 Larger electrodes of sponge cadmium were prepared from thecadmium oxide nickel mixture in the manner described under Cell No. l,in order to determine whether these could satisfactorily be cut intosmaller pieces for cell assembly. The first electrode formed was a flatplate of dimensions 125 X 60 X 6 mm which was held in a nickel foilcontainer for electrolytic reduction. The surface layers of spongecadmium tended to break away from the balance of the plate, but resultsindicated that with suitable quality control in the preliminary shapingof the cadmium oxide-nickel powder slab the material could be handledwith ease. The second electrode prepared was in the form of a 1 Va inchdiameter round bar of length 6 inches prepared in a nickel mesh basket.This electrode was formed as a source of disc shaped electrodes, and wasgiven a preliminary discharge at the 100-hour rate and delivered 85% ofthe theoretical electrode capacity. The electrode was subsequentlyrecharged and sliced into discs.

The experiments hereinbefore described indicated furthermore that cellsusing sponge cadmium electrodes prepared according to the presentinvention show good low temperature operation, particularly bycomparison with corresponding batteries using zinc cathodes. Moreover,the long-term stability of the cells important for shelf life, makesthem an attractive commercial proposition as primary batteries.

What we claim as our invention is:

1. A process for the preparation of sponge cadmium electrode materialwhich comprises the steps of compressing a mixture of cadmium oxide andfinely divided electronic conductor, said electronic conductor beingpresent in an amount of 5 to 25 percent by weight of the total mixture,and being inert towards alkaline electrolytes, at a pressure of at least1 psi but not exceeding psi, providing an electrical connection to saidcompressed mixture, and subsequently electrolytically reducing saidcadmium oxide in an alkaline electrolyte.

2. A process as claimed in claim 1 wherein said finely dividedelectronic conductor is finely powdered nickel.

3. A process as claimed in claim 2 in which said finely powdered nickelis a nickel powder having an apparent density less than 2 gm/cm and ispresent in an amount of between 10 and 25 percent by weight of the totalmixture.

4. A process as claimed in claim 3 wherein said nickel powder has anapparent density less than 1 gm/cm.

5. A process as claimed in claim 4 in which said cadmium oxide is apowder of particle size between about 50 microns and about microns.

6. A process as claimed in claim 3 wherein the cad mium oxide is apowder of particle size between about 50 microns and 150 microns andwherein the electronic conductor is finely powdered nickel of apparentdensity less than 1 gm/cm.

7. A process as claimed in claim 1 wherein said pressure is between 1and 4 psi.

8. A process as claimed in claim 7 wherein said cadmium oxide is apowder of particle size less than microns.

9. A process as claimed in claim 7 wherein said cadmium oxide is apowder of particle size between about 50 microns and about 150 microns.

10. A process as claimed in claim 1 wherein said finely dividedelectronic conductor is a metal in filamentary form.

11. A process as claimed in claim 10 wherein the metal in filamentaryform is steel wool, nickel wool or electrolytic copper wool.

12. A process as claimed in claim 1 wherein after reduction of thecadmium oxide the material is subsequently cut or shaped to theconfiguration and size required of the final electrode.

13. A process as claimed in claim 1 wherein the mixture of cadmium oxideand electronic conductor is compressed to form an electrode of theconfiguration and size required of the final electrode.

UNiTED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,775,273 DatedNovember 27, 1973 Inventor(s) H -n68, Ronald L- etc- Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

In the heading, between the filing data for the application and theinternational class data, insert:

'-Claims priority, application Canada,

filed-January 24-, 1969, 4l,l00-

Signed and sealed this 16th day QfJuly 1971+.

(SEAL) Attest:

McCOY M. GIBSON, JR. c. MARSHALL DANN Attesting Officer Commissioner ofPatents :QRM PC4050 USCOMM-DC 60376-P69 U.5. GOVERNMENT PRINTING OFFICE:1969 0-366-334,

2. A process as claimed in claim 1 wherein said finely dividedelectronic conductor is finely powdered nickel.
 3. A process as claimedin claim 2 in which said finely powdered nickel is a nickel powderhaving an apparent density less than 2 gm/cm3 and is present in anamount of between 10 and 25 percent by weight of the total mixture.
 4. Aprocess as claimed in claim 3 wherein said nickel powder has an apparentdensity less than 1 gm/cm3.
 5. A process as claimed in claim 4 in whichsaid cadmium oxide is a powder of particle size between about 50 micronsand about 150 microns.
 6. A process as claimed in claim 3 wherein thecadmium oxide is a powder of particle size between about 50 microns and150 microns and wherein the electronic conductor is finely powderednickel of apparent density less than 1 gm/cm3.
 7. A process as claimedin claim 1 wherein said pressure is between 1 and 4 psi.
 8. A process asclaimed in claim 7 wherein said cadmium oxide is a powder of particlesize less than 175 microns.
 9. A process as claimed in claim 7 whereinsaid cadmium oxide is a powder of particle size between about 50 micronsand about 150 microns.
 10. A process as claimed in claim 1 wherein saidfinely divided electronic conductor is a metal in filamentary form. 11.A process as claimed in claim 10 wherein the metal in filamentary formis steel wool, nickel wool or electrolytic copper wool.
 12. A process asclaimed in claim 1 wherein after reduction of the cadmium oxide thematerial is subsequently cut or shaped to the configuration and sizerequired of the final electrode.
 13. A process as claimed in claim 1wherein the mixture of cadmium oxide and electronic conductor iscompressed to form an electrode of the configuration and size requiredof the final electrode.